Hair, protein filaments covering the skin of mammals, including humans, plays a pivotal role in skin protection, thermoregulation and touch sensing. Being one of the most visible human features, hair pigmentation can be modified using colorants and many commercial coloring formulations serve this cosmetic purpose. However, there is a contradiction in many conventional hair coloring techniques. On the one hand, the technique requires skin friendly aqueous dye solutions, and on the other hand, after application, the dye adsorbed on to hair has to be insoluble and as a practical matter, be able to survive at least 10 shampoo washes. These requirements are usually met with different chemical reactions involving the addition of H2O2 or other chemicals to color formulations, which are not healthy for hair and often cause allergic responses.
Another aspect of hair in humans and other mammals is that the hair may be affected by numerous diseases and parasites. Fungal diseases, mites, lice and fleas depend on hair serving as a shelter and breeding habitat. Although parasites such as lice are less common in industrial nations, they still pose a significant threat in developing countries, affecting millions. An effective therapy to eliminate these parasitic pests is required. However, a direct medical treatment is often difficult due to the complexities of providing sustain drug delivery onto hair.
Hair has a complicated chemical composition and its microstructure looks like attached flakes with narrow gaps called cuticles. The cuticles-cortex composite structure serve as binding sites for targeted interactions to adsorb drugs or dye. Lasting hair treatments like conditioners are focused at surface binding driven by charge or applied to the inter-cuticle spaces, in order to provide enhanced absorption into the cortex. Such formulations often disturb the natural chemistry of hair, causing dryness, oxidation and discoloration. An improved, longer-lasting, less damaging technique for applying both colorants and medicines to hair would be a significant improvement in the art.